Attaching components to a printed circuit card

ABSTRACT

Coupling components to an underlying substrate using a composition of a polymer and magnetic material particles. Upon applying the composition between the component and the printed circuit board, the composition may be subjected to a magnetic field to align the magnetic material particles into a conductive path between the component and the underlying substrate. At the same time the polymer-based material may be cured or otherwise solidified to affix the conductive path formed by the magnetic material particles.

BACKGROUND

[0001] The present invention relates to circuit components and, inparticular, to attaching components to underlying substrates.

BACKGROUND OF THE RELATED ART

[0002] There may be several techniques for attaching components, such asan integrated circuit, to underlying substrates, such as printed circuitcards. However, these techniques may have multiple problems. Forexample, eutectic lead solder may be used to attach a component to anunderlying substrate because the eutectic lead solder has a low meltingtemperature and good viscosity, but environmental regulations may forcelead solders to be phased out of manufacturing. Other solders that donot contain lead, including, but not limited to, tin alloys, may be usedto connect components to underlying substrates. However, these soldershave high melting temperatures that may damage the components orunderlying substrates during the process of attaching them together.Other methods of attaching components and underlying substrates, such ascup and cone suspension, may have contact resistance problems betweenthe surfaces of the component and the underlying substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The invention may best be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

[0004]FIG. 1 shows an embodiment of the invention having an underlyingsubstrate coupled to a component by a solidified bi-materialcomposition;

[0005]FIG. 2 shows an embodiment of the invention having an underlyingsubstrate and screen pads;

[0006]FIG. 3 shows an embodiment of the invention having an underlyingsubstrate, a component, and a non-solid bi-material composition;

[0007]FIG. 4 shows an embodiment of the invention in the form of anunderlying substrate, a component, and a bi-material composition in thepresence of a magnetic field and ultraviolet light;

[0008]FIG. 5 shows an embodiment of the invention having an underlyingsubstrate coupled to a component by a solidified bi-materialcomposition; and

[0009]FIG. 6 shows an embodiment of the invention in the form of aflowchart of a method for forming the conductive path between thecomponent and the underlying substrate.

DETAILED DESCRIPTION

[0010] The following description makes reference to numerous specificdetails in order to provide a thorough understanding of the presentinvention, however, it is to be noted that not every specific detailneed be employed to practice the present invention. Additionally, wellknown details, such as particular materials or methods have not beendescribed in order to avoid obscuring the present invention.

[0011] Referring to FIG. 1, an embodiment of the invention is shown inthe form of an underlying substrate 101 coupled to a component 111 by aconductive solidified bi-material composition 113 and 115. Thebi-material composition 113 and 115 may first be subjected to a magneticfield in order to align the magnetic material particles 121 into aconductive path. The composition 113 and 115 may then be solidified inorder to fix the conductive paths of the magnetic material particles121. The magnetic material particles 121 may form a conductive paththrough the polymer-based material 117 and 119 from the component 111 tothe screen pads 103 and 105 coupled to the underlying substrate 101. Thescreen pads 103 and 105 may be coated with pre-coating layers 107 and109.

[0012] Referring to FIG. 2, an embodiment of the invention is shown inthe form of an underlying substrate 101 and screen pads 103 and 105pre-coated with a conductive composition. The underlying substrate 101may be a substrate such as, but not limited to, a printed circuit card,an aluminum lead frame, and a fine-pitched ball grid array. A component(not shown) such as, but not limited to, an integrated circuit, may becoupled to the underlying substrate 101 through screen pads 103 and 105and a bi-material composition (not shown). The screen pads 103 and 105,shown in FIG. 2, may be electrically coupled to the underlying substrate101. A conductive composition may be used to pre-coat the screen pads103 and 105 before coupling the component to the underlying substrate101. In this illustrated embodiment, the conductive composition used topre-coat the screen pads 103 and 105 is the same bi-material compositionused to establish a conductive path between the component and theunderlying substrate 101. Pre-coating layers 107 and 109 may make thesurface of the screen pads 103 and 105 more adherable for laterdeposition of the bi-material composition. If the bi-materialcomposition is used for pre-coating layers 107 and 109, it may not becured or solidified before coupling the component to the underlyingsubstrate 101. While the pre-coating layers 107 and 109 are shown inFIG. 2, in order to perform the invention, the pre-coating layers 107and 109 may be omitted in some embodiments.

[0013] In one embodiment of the invention, the bi-material compositionmay be formed by mixing a polymer-based material with magnetic materialparticles. The polymer-based material may be a polymer, including, butnot limited to, conductive polymers, thermoplastic polymers, andthermoset polymers. Some specific polymer-based materials that may beused include, but are not limited to, polyamide, ultraviolet lightcurable epoxies, and photo-resist polymers. In one embodiment, apolymer-based material, such as but not limited to photo-resist, mayhave approximately the same coefficient of thermal expansion as theunderlying substrate 101. Having approximately the same coefficient ofthermal expansion may increase the reliability of the interface betweenthe polymer-based material of the bi-material composition and theunderlying substrate 101. Otherwise, the greater the difference betweenthe coefficients of thermal expansion between polymer-based material andthe underlying substrate 101, the greater the difference of contractionor expansion between the two during temperature changes andcorrespondingly, more fatigue may be experienced at the interfacebetween polymer-based material and the underlying substrate 101.

[0014] The magnetic material particle may be a material, including, butnot limited to, ferro-magnetic metal, magnetic ceramics, andferro-electric materials. Materials that may be used, include, but arenot limited to, iron, barium strontium titanate, strontium tantalumoxide, and peroskovites. In addition, magnetic material particles may bemade out of magnetite or metallic materials with low magneticretentivity. Magnetic material particles may be small in size andacicular shaped (i.e. with a high aspect ratio morphology). In oneembodiment, the approximate dimensions of a magnetic material particlemay be one micron by two microns by ten microns. However, otherdimensions may also be within the scope of the invention.

[0015] Several by-weight ratios of the polymer-based material andmagnetic material particles in the bi-material composition are withinthe scope of the invention. For example, in one embodiment, thepolymer-based material may constitute approximately 40% by weight of thebi-material composition, while the magnetic material particles mayconstitute approximately 60% by weight. Other by-weight percentages maybe used, depending on several factors, including, but not limited to,the type of polymer-based material, the type of magnetic materialparticles used, and the size of the magnetic material particles used.

[0016] Magnetic material particles may need to be mixed uniformly intothe polymer-based material. Therefore, if the polymer is athermoplastic, the polymer may be in liquid form when mixed with themagnetic material particles, and if the polymer is a thermoset polymer,the polymer may be in a soft, or liquid, uncured form when mixed withthe magnetic material particles. After forming the bi-materialcomposition by mixing the polymer-based material and the magneticmaterial particles together, the bi-material composition may be putthrough a screen onto the screen pads. The screen may act as a stencilto control the volume and placement of the bi-material composition ontothe underlying substrate 101. To put the bi-material composition throughthe screen, the holes in the screen may be lined up with the areas orcomponents where the bi-material composition is to be deposited, and asqueegee may be used to push it through the screen in a screen printingprocess. The screen may allow the location and amount of bi-materialcomposition being deposited to be controlled. Other methods of puttingthe bi-material composition through the screen, including, but notlimited to, pulling the bi-material composition through the screen witha magnet or vacuum, may also be within the scope of the invention. Othermethods of depositing the bi-material composition into a pre-coatinglayer 107 and 109 on the screen pads 103 and 105 may also be within thescope of the invention. For example, in one embodiment, the bi-materialcomposition may be deposited directly without the use of a screen.

[0017] Referring to FIG. 3, an embodiment of the invention is shown inthe form of an underlying substrate 101, a component 111, and anon-solid bi-material composition 113 and 115. The underlying substrate101 may be coupled to screen pads 103 and 105. The bi-materialcomposition 113 and 115 may be used to form a precoating layer 107 and109 on the screen pads 103 and 105. The bi-material composition 113 and115 may be deposited on the screen pads 103 and 105 before the component111 is placed on the underlying substrate 101. In another embodiment ofthe invention, the component 111 may be placed onto the screen pads 103and 105 before the bi-material composition 113 and-115 is deposited. Inaddition, while the bi-material composition 113 and 115 is shown on theside and on top of the component 111 in the illustrated embodiment ofFIG. 3, in another embodiment, the bi-material composition 113 and 115may be confined to the sides or confined to the sides and bottom of thecomponent 111. When first deposited, the bi-material composition 113 and115 may be in a liquid state with magnetic material particles 121 inrandom arrangement in the polymer-based material 117 and 119.

[0018] Referring to FIG. 4, an embodiment of the invention is shown inthe form of a underlying substrate 101, a component 111, and abi-material composition 113 and 115 being exposed to a magnetic fieldand UV light. In the embodiment shown in FIG. 4, an underlying substrate101 may be coupled to a component 111 through screen pads 103 and 105 bya bi-material composition 113 and 115 with magnetic material particles121. Upon application of the magnetic field, which may be provided bymagnets 403 and 405, the magnetic material particles 121 may group andalign with each other to form a magnetic material particle path. Themagnetic material particles 121 in the bi-material composition 113 and115 may be acicular in shape. The magnetic material particles 121 may belong, thin, and flat to increase the number of surface contact pointsthat may improve the conductive path formation.

[0019] The magnetic field strength used may be less than a level thatmay cause sensitive devices on or near the underlying substrate 101 tobe affected by soft errors. For example, while a weaker magnetic fieldmay be needed near central processing units, a stronger magnetic fieldmay be used for passive components such as capacitors and resistors.While magnets 403 and 405 are shown to supply the magnetic field, othersources of magnetic fields including, but not limited to natural magnetsand electro-magnets, may also be within the scope of the invention.

[0020] A secondary magnetic attraction from metallic surfaces on thecomponent 111 may bend the magnetic material particle path enough toform a conductive path between component 111 and screen pads 103 and105. In the context of the invention, ‘bend’ means that the lines ofmagnetic flux are affected by the secondary magnetic attraction frommetallic surfaces, so that the magnetic material particle path isdirected to the metallic surfaces of component 111.

[0021] While the magnetic field is being applied, a UV light from a UVlight source, such as UV light sources 401 and 407, may be applied tothe bi-material composition 113 and 115. While the UV light 401 and 407cures the bi-material composition 113 and 115, causing it to stiffen,the magnetic material particles 121, under the influence of the magneticfield, may form conductive paths and eventually be trapped in thesolidified polymer-based material in conductive pathways between thecomponent 111 and the screen pads 103 and 105.

[0022] While UV lights 401 and 407 are shown in the embodiment of theinvention, other lights such as, but not limited to, regular light andinfrared light, may also be used to cure the polymer-based material 117and 119 in the bi-material composition 113 and 115. Heat sources mayalso be used to cure the polymer-based material 117 and 119 byincreasing the polymer-based material's temperature. In addition tousing lights 401 and 407 or neat sources, the polymer-based material 117and 119 may also be cured by using a curing agent mixed into thebi-material composition 113 and 115 at the time the magnetic field isapplied. Other methods of curing the polymer-based material 117 and 119may also be within the scope of the invention. In other embodiments ofthe invention, the polymer-based material 117 and 119 may be athermoplastic polymer. For thermoplastic polymers, instead of applyingUV lights 401 and 407 or a curing agent, a heat source may used toliquefy the polymer-based material 117 and 119 and then the heat sourcemay be removed. In another embodiment of the invention, thethermoplastic polymer may be solidified by lowering its temperature.

[0023] Several factors may also affect the formation of conductive pathsbetween the component 111 and the screen pads 103 and 105. For example,the viscosity of the polymer-based material 117 and 119, the density ofthe magnetic material particles 121, the shape of the magnetic materialparticles 121, the distribution of the magnetic material particles 121,the concentration of the magnetic material particles 121 in thebi-material composition 113 and 115, and the temperature conditionsduring the application of the magnetic field may affect the speed atwhich the magnetic material particles 121 align and form a conductivepath between the component 111 and the underlying substrate 101.

[0024] For example, if the viscosity of the bi-material composition 113and 115 is too high, the magnetic material particles 121 may not be ableto move into alignment before the polymer-based material 117 and 119solidifies. However, if the viscosity of the bi-material composition 113and 115 is too low, the magnetic material particles 121 may move quicklyinto position and then slightly disjoin in a random alignment accordingto the magnetic field. The higher the viscosity of the polymer-basedmaterial 117 and 119, the higher the attraction force may be betweenclose adjacent magnetic material particles 121. However, with a lowviscosity polymer-based material 117 and 119, the magnetic materialparticles 121 may be more influenced by the magnetic force of themagnets 403 and 405 than the attraction force between them and may beslightly pulled away from each other to align with the magnetic field.In a high viscosity polymer-based material 117 and 119, the magneticmaterial particles 121 may have a stronger attraction at close rangethan the magnetic force pulling them into alignment. The viscosity ofthe bi-material composition 113 and 115 may need to be adjusted to allowthe attraction between each magnetic material particle 121 to influencethe magnetic material particles 121 into forming a path and bendingbetween the component 111 and the screen pads 103 and 105. Similarproblems may occur if the shapes of the magnetic material particles 121are too big or too small or if their density and concentration is toogreat or too small.

[0025] Referring to FIG. 5, an embodiment of the invention is shown inthe form of an underlying substrate 101 coupled to a component 111 by aconductive solidified bi-material composition 113 and 115. In theembodiment shown in FIG. 5, the bi-material composition 113 and 115 maybe subjected to a magnetic field in order to align the magnetic materialparticles 121 into a conductive path. Then the composition 113 and 115may be solidified in order to fix the conductive paths of the magneticmaterial particles 121. The magnetic material particles 121 may form aconductive path through the polymer-based material 117 and 119 from thecomponent 111 to the screen pads 103 and 105 coupled to the underlyingsubstrate 101.

[0026] While one component 111 is shown in the embodiment in FIG. 5,multiple components may be coupled to the underlying substrate 101 usingthe invention. Components 111 may be applied at the same time, or thecomponents 111 may be applied one at a time. In another embodiment ofthe invention, the components 111 may be applied in shifts, by which aselected type of component 111 is applied to the underlying substrate101 in each shift. While setting the bi-material composition 113 and 115on the selected type of components 111, a magnetic field with a strengthsufficient for the specific amount and type of bi-material composition113 and 115 used with the selected components 111 may be applied atapproximately the same time the polymer-based material 117 and 119 issolidified. For example, bigger components 111 may require morebi-material composition 113 and 115 to form the appropriate conductiveconnections, and with bigger components 111, there may be morebi-material composition 113 and 115 to solidify and more magneticmaterial particles 121 to align. The magnetic field strength and methodof solidifying the polymer-based material 117 and 119 may need to beadjusted for the components 111 using a greater amount of bi-materialcomposition 113 and 115. After the conductive connections are formed inthe bi-material composition 113 and 115, the component connection to theunderlying substrate 101 may be electrically tested.

[0027] Referring to FIG. 6, a flowchart of a method of an embodiment ofthe invention is shown for electrically coupling a first component to asecond component. At block 601, a bi-material composition of magneticmaterial particles and a polymer-based material may be mixed. At block603, the bi-material composition may be put through a screen. At block605, a first component, such as, but not limited to, an underlyingsubstrate, may be pre-coated with a layer of conductive composition. Atblock 607, the bi-material composition may be deposited on a firstcomponent. At block 609, a second component may be placed onto a firstcomponent at the site where the bi-material composition is deposited. Atblock 611, a magnetic field may be applied to the bi-materialcomposition to form an aligned path of the magnetic particles and bendsaid aligned path of magnetic material particles to form part of aconductive path between the first component and the second component. Atblock 613, the polymer-based material may be solidified. For example, acuring compound or UV light source may be applied if the polymer-basedmaterial is a thermoset polymer. At block 615, after the polymer-basedmaterial has been solidified and the magnetic material particles havebeen fixed in the bi-material composition, the conductive path formed bythe magnetic material particles between the first component and thesecond component may be tested.

[0028] Although an exemplary embodiment of the invention has been shownand described in the form of a method for attaching components to anunderlying substrate, many changes, modifications, and substitutions maybe made without departing from the spirit and scope of the claimedinvention.

We claim:
 1. An apparatus comprising: a polymer-based material; and aplurality of magnetically aligned magnetic material particles in saidpolymer-based material that form an electrically conductive path througha part of said polymers based material.
 2. The apparatus of claim 1wherein said polymer-based material is selected from a group consistingof conductive; polymers, thermoplastic polymers, and thermoset polymers.3. The apparatus of claim 1 wherein said polymer-based material is apolyamide.
 4. The apparatus of claim 1 wherein said polymer-basedmaterial is an ultra-violet light curable epoxy.
 5. The apparatus ofclaim 1 wherein said magnetic material is selected from a groupconsisting of ferro-magnetic metal, a magnetic ceramic, and aferro-electric material.
 6. The apparatus of claim 1 wherein saidapparatus is comprised of approximately 40 percent by weightpolymer-based material and approximately 60 percent by weight magneticmaterial particles.
 7. The apparatus of claim 1 wherein said magneticmaterial particles are acicular shaped.
 8. The apparatus of claim 1wherein said polymer-based material is a photo-resist material.
 9. Theapparatus of claim 1 wherein said magnetic material particles are toform part of the electrically conductive path from a component to anunderlying substrate.
 10. The apparatus of claim 1 wherein dimensions ofthe magnetic material particles are approximately one micron by twomicrons by ten microns.
 11. The apparatus of claim 1 wherein saidmagnetic material is selected from a group consisting of iron, bariumstrontium titanate, strontium tantalum oxide, and peroskovites.
 12. Amethod comprising: mixing a composition of magnetic material particlesand a polymer-based material; depositing said composition onto a firstcomponent; placing a second component onto said first component at asite of the deposited composition; applying a magnetic field to saidcomposition, to form an aligned path of said magnetic material particlesand to bend said aligned path of magnetic material particles to formpart of a conductive path between said first component and said secondcomponent; and solidifying said polymer-based material.
 13. The methodof claim 12 further comprising putting said composition through a screenbefore said depositing.
 14. The method of claim 13 wherein said puttingincludes using a squeegee.
 15. The method of claim 12 further comprisingpre-coating said first component before said depositing.
 16. The methodof claim 15 wherein said pre-coating comprises applying a thin layer ofsaid composition.
 17. The method of claim 12 further comprising testingthe conductive path between said first component and said secondcomponent.
 18. The method of claim 12 wherein said solidifying includesapplying an ultra-violet light to said composition.
 19. The method ofclaim 12 wherein solidifying includes changing said polymer-basedmaterial's temperature.
 20. The method of claim 12 wherein saidpolymer-based material is solidified and said magnetic field is appliedat approximately a same time.
 21. The method of claim 12 whereinapplying a magnetic field includes using the magnetic field from ametallic surface to bend the aligned path.
 22. The method of claim 12wherein mixing includes mixing the composition of magnetic materialparticles having dimensions of approximately one micron by two micronsby ten microns.
 23. A system comprising: a substrate; a componentcoupled to said substrate; and a composition of magnetic materialparticles and a polymer-based material coupled to said component andsaid substrate
 24. The system of claim 23 further comprising screen padscoupled to said substrate.
 25. The system of claim 23 wherein saidmagnetic material particles include a conductive path between saidcomponent and said substrate.
 26. The system of claim 23 wherein saidsubstrate is selected from a group consisting of printable circuitboards, aluminum lead frames, and fine pitch ball grid arrays.
 27. Thesystem of claim 23 wherein said composition is comprised ofapproximately 40 percent by weight of the polymer-based material andapproximately 60 percent by weight of the magnetic material particles.28. The system of claim 23 wherein said magnetic material particles areacicular shaped.
 29. The system of claim 23 wherein said polymer-basedmaterial is a photo-resist material.
 30. The system of claim 23 whereina coefficient of thermal expansion of the polymer-based material isapproximately equal to a coefficient of thermal expansion of thesubstrate.